Combination manhole cover and safety valve



NOV# 27, 1934. R, NEREM 1982,118

COMBINATION MANHOLE COVER AND SAFETY VALVE Filed Aug. 25, 1931 Patented Nov. v.1?7, l 934 NITED STATES CMBINATION MANHOLE COVER SAFETY VALVE Robert Nerem, Evanston, ill., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application August 25,

Claims.

This invention relates to a combination manhole cover and safety valve for use on containers or tanks containing gases or volatile materials Such as gasoline and the like.

" When gasoline storage tanks are heated to high temperatures, due to nearby res, the gasoline volatilizes and causes considerable pressure to develop within the tank, and a safety pressure valve must be provided on the tank to release E@ the gases, otherwise the tank may blow-up.

The object of my invention is to provide a manhole cover with the dual function of forming a substantially gas tight cover for the manhole and a safety valve to release the volatile constituents from the container when the pressure within the container has risen above a predetermined pressure tolera-nce. f

A further object is to provide a simple and efhcient safety valve that is free from the un- 2@ desirable feature of sticking; a defect which is common among the valves now in use.

The construction and operation of my combination manhole cover and safety valve will be apparent from the following description when read in connection with the drawing, in which:

Figure 1 is a vertical cross section of the com-- bination manhole cover and safety valve.

Figure 2 is a top plan view of Figure 1.

The manhole comprises a manhole-ring projecting through the roof of the tank 11 and corn- Inunicating with the space above the tank, or the atmosphere, and the interior of the tank. The manhole cover 12, which seats upon the manhole-ring, is a lat disc with its edge extending beyond the end of the manhole-ring. Preferably the edge is beveled downwardly as shown at 13. The circular contact surface on the manhole ring, as shown at 14, is ground to give a substantially gas tight joint between the cover and manholering.

A trough 15 is rigidly fastened around the exterior of the manhole-ring and surrounds the manhole cover. Drain slots 15a are cut in the side of the trough near the bottom, thereby providing a drain for the rain water. The side of the trough terminates in two flanges 16 which form a part of a hinge to be described hereinafter. This trough, or deflector, serves to deflect the gases upwardly as they are released from the manhole ring and prevents them from settling on, or rolling along, the top of the tank. If the gases ignite while in contact with the roof, the heat absorbed by the tank the heat absorbed if the of Contact with the tank.

gases were ignited out Also the nre hazard would be greater than 1931, Serial No. 559,182 (Cl. 2220-44) is materially reduced when the of contact with the tank.

The hinge for the cover comprises a flat member 1'7 brazed or fastened to the cover 12 and pivoted on the bolt 18. The bolt rests in the vertical slots 19 which are contained in the flanges 16. The bolt is prevented from sliding out of the slots by the nut 20. By having the bolt slidably mounted in the slot 19, the cover andl bolt can be raised by the pressure of the Volatile gases within the tank, thereby permitting the gases to escape through the circumferential opening formed between the beveled edge of the top and the manhole-ring when the cover is unseated.

A hasp 21 is rigidly fastened to the cover 12, and a hole 21a is provided in the hasp which gases burn out enables it to slide over the member 22, thereby l affording a means to lock the cover by placing a lock 22a through the hole 23. When it is desired to inspect the interior of the tank, the lock is removed from the hole in the member 22, and the top is lifted by the hasp. During this operation the hinge pivots on the bolt 18 that rests in the bottom of the slots 19.

A circular ring 24 is rigidly fastened around the interior of the manhole-ring and supports a screen 25 which prevents extraneous. materials from falling into the tank when the top is opened.

When the cover 12 is seated, as shown in Figure 1, the gases within the tank exert their force upon that area ofthe top which is equivalent to the cross sectional area of the manhole-ring 10. When the manhole cover is unseated, the gases within the tank are released through the circumferential opening which is formed between the cover and man-hole ring, and as the gases escape from the tank they strike the beveled edge 13 and exert a lifting force on the cover 12. While the cover is unseated, the area upon which the escaping gases exert their force is greater thanthe area upon which the gases acted when the top was closed. Therefore, the pressure per unit area necessary to keep the cover unseated is less than the pressure per unit area required to unseat the cover. Also, the escape of the gases from the circumferential opening around the manhole ring is somewhat retarded by causing the gases to expand into the auxiliary vchamber 26 that is formed between the trough and the edge of the cover. By the use of this structure, the gases exert a greater lifting force on the edge of the cover than would be possible if the escape of -the gases into the atmosphere was unobstructed. Since the pressure at which the cover will unseat is determined by the weight of the cover, weights may be placed on thecover to increase its weight, or the cover may be constructed of material` that will give the desired Weight. I have found it very easy to construct covers that permit the safety valve to pop-off when the pressure within the tank reaches some predetermined pressure between the range of twenty-five to forty pounds per square foot, but my invention is not limited in its use to the above range of pressures. 'In the operation of the combination manhole and safety valve, the cover remains seated upon the gas tight joint until the force of the gases within the tank slightly exceed the weight of the top. Then the top and hinge are displaced vertically, and the gases are permitted to escape until the force of the escaping gases can no longer'support the top. The cover quickly reseats itself and remains closed until the pressure within the-tank builds up to a point that slightly exceeds the weight of the cover.

The use of this combination of large pressure area exposure when the top is unseated and small pressure area exposure when the top vis seated,

permits the pressure within the tank to fall much below the pressure that is required to unseat the cover, before the cover reseats. The effect of this construction is to prevent the closing and opening, or fluttering, of the top when the pressure within the tank falls slightly below the pressure required to unseat the cover. By enabling the pressure within the tank to fall much below the pressure required to unseat the cover, the cover quickly reseats itself, and immediately cuts off the escaping vapors. This mode of operation is desirable because the vapors usually ignite as they rise above the top of the tank, and a slow closing cover would permit the flames to burn back into the tank and ignite the contents therein.

In constructing the combination manhole cover and safety valve, the vertical side of the trough should be long enough to project above the manhole cover, when said cover is unseated, and the clearance between the manhole cover and the side of the trough should be small.' A structure of these proportions would prevent a thief from passing a' hose under the top and siphoning the gasoline from the tank. Also, the screen in the manhole-ring may prevent the hose from Vreaching the gasoline if an entrance is effected.

My invention has proved to be very satisfactory in service, it is very simple in structure and made` of few movable parts, it has a dualfunction of operating as a manhole cover anda safety valve, it hasa quick reseating action, and is free from a complicated valve structure that might stick and cause excessive pressure to develop within the tank during a re.

- tile liquids, characterized by a The above results are accomplished in a satisfactory manner by the but it will be obvious that changes may be made without departing from the scope of the invention.

1. A combination manhole and safety 1 valve, characterized by a manhole-ring, a fiat, continuous cover for said manhole-ring, said cover forming a substantially gas tight joint with said manhole-ring and extending beyond said ring, a deector attached to the exterior of said manholering, and a hinge attached to said cover and slidably mounted in aslot contained in said deiiector.

2. A combination manhole and safety valve, comprising a manhole-ring, a flat-continuous cover forsaid manhole-ring, the edge of said cover extending beyond the ring, a trough surrounding said cover and terminating in two slotted members, and a hinge connected to said cover and slidably mounted in said slots.

3. A combination manhole cover and safety' valve for use on containers, comprising a conduit for communicating with the interior of a container, a fiat cover for said conduit, said cover forming a substantially gas tight joint with said conduit and extending beyond the periphery of raid conduit, a deflector attached to the exterior of said conduit, and a hinge attached to said cover and slidably mounted in a slot contained in said deflector.

4. A combination manhole cover and safety valve, characterized by a manhole-ring, a cover for said manhole-ring, said cover forming a substantially gas tight joint with said manhole ring and extending beyond said ring, a deflector attached to the exterior of said manhole-ring, and a hinge attached to said cover and slidably mounted in\a slot contained in said deector.

5. A combination manhole and safety valve for use on a storage container for gases or volamanhole-ring,v a flat cover for said manhole-ring, said cover forming a substantially gas tight joint with said manhole-ring and exposing a larger surface area to` the escapng gases when unseated than is exposed to the gaseswithin the storage container when the cover is seated, a deflector attached to the exterior of said manhole-ring, and a hinge a slotcontained in said deflector.

ROBERT NEREM,

apparatus as disclosed.,` 

